Leakage Causes Analysis of Water Wall-cooled Tube in one Power Plant
Macroscopic inspection,spectral inspection,microstructure analysis,hardness testing,and mechanical performance testing were conducted on samples of leaking water-cooled wall tube in a power plant.The burst is large and there is obvious deformation and thinning at the edge of the burst.The chemical composition of the first explosive tube meets the standard requirements.The structure on the facing smoke side of the first blast tube is composed of ferrite and elongated pearlite,with no dispersed characteristics of pearlite,which is a phase transformed microstructure.The struc-ture on the back smoke side is composed of ferrite and pearlite too,aged at level 3.The hardness value on the facing smoke side is higher than that on the back smoke side.The reason for the leak-age of the water-cooled wall tube is that the tube overheats for a short period of time,causing the temperature on the upstream side of the tube to exceed the Ac3 temperature,resulting in a phase transition of the microstructure on the upstream side of the tube and a decrease in mechanical prop-erties.Under the action of steam internal pressure,the upstream side of the tube with higher tem-perature and more decreased performance undergoes bulging and deformation,causing the tube wall to become thinner and ultimately leading to tube bursting.
water-cooled wall tubephase transformed microstructureblocked by matters-boresshort term overheating